Multi-channel network monitoring apparatus, signal replicating device, and systems including such apparatus and devices, and enclosure for multi-processor equipment

ABSTRACT

A multi-channel network monitoring apparatus has input connectors for network signals to be monitored and four channel processors in a rack-mountable chassis/enclosure for receiving and processing a respective pair of incoming signals to produce monitoring results. Each processor operates independently of the others and is replaceable without interrupting their operation. LAN connectors enable onward communication of the monitoring results. A cross-point switch routes each incoming signal to a selected processor and can re-route a channel to another processor in the event of processor outage. Each processor has a self-contained sub-system of processing modules interconnected via a CPU-peripheral interface in a backplane, which provides a separate peripheral interface for each processor. The backplane provides locations for processors to lie horizontally across a major portion of the backplane area facing the front of the enclosure, and a location for an interface module over a minor portion of that area facing the rear, so as to provide external connectors at the rear of the enclosure. A power supply module is positioned over another portion of the backplane area, on the same side as the interface module. The location of the power supply module behind the backplane saves height and/or width in the rack.

INTRODUCTION

The invention relates to telecommunications networks, and in particularto apparatus and systems for monitoring traffic in broadband networks.

In telecommunication networks, network element connectivity can beachieved using optical fibre bearers to carry data and voice traffic.

Data traffic on public telecommunication networks is expected to exceedvoice traffic with Internet Protocol (IP) emerging as one datanetworking standard, in conjunction with Asynchronous Transfer Mode(ATM) systems. Voice over IP is also becoming an important applicationfor many Internet service providers with IP switches connecting IPnetworks to the public telephony network (PSTN). IP can be carried overa Sonet transport layer, either with or without ATM. In order tointer-operate with the PSTN, IP switches are also capable ofinter-working with SS7, the common signalling system fortelecommunications networks, as defined by the InternationalTelecommunications Union (ITU) standard for the exchange of signallingmessages over a common signalling network.

Different protocols are used to set up calls according to network typeand supported services. The signalling traffic carries messages to setup calls between the necessary network nodes. In response to the SS7messages, an appropriate link through the transport network isestablished, to carry the actual data and voice traffic (the payloaddata) for the duration of each call. Traditional SS7 links are timedivision multiplexed, so that the same physical bearer may be carryingthe signalling and the payload data. The SS7 network is effectively anexample of an “out of band” signalling network, because the signallingis readily separated from the payload. For ATM and IP networks, however,the signalling and payload data is statistically multiplexed on the samebearer. In the case of statistical multiplexing the receiver has toexamine each message/cell to decide if it is carrying signalling orpayload data. One protocol similar to SS7 used in such IP networks isknown as Gateway Control Protocol (GCP).

The monitoring of networks and their traffic is a fundamentalrequirement of any system. The “health” of the network must bemonitored, to predict, detect and even anticipate failures, overloadsand so forth. Monitoring is also crucial to billing of usage charges,both to end users and between service providers. The reliability(percentage availability) of monitoring equipment is a prime concern forservice providers and users, and many applications such as billingrequire “high availability” monitoring systems, such that outages, dueto breakdown or maintenance, must be made extremely rare.

A widely-used monitoring system for SS7 signalling networks is acceSS7 ™from Agilent Technologies (and previously from Hewlett-Packard). Aninstrument extracts all the SS7 packetised signals at SignallingTransfer Points (STPs), which are packet switches analogous to IProuters, that route messages between end points in SS7 networks. Theneed can be seen for similar monitoring systems able to cope withcombined IP/PSTN networks, especially at gateways where the twoprotocols meet. A problem arises, however, in the quantity of data thatneeds to be processed for the monitoring of IP traffic. In InternetProtocol networks, there is no out of band signalling network separatefrom the data traffic itself. Rather, routing information is embedded inthe packet headers of the data transport network itself, and the fulldata stream has to be processed by the monitoring equipment to extractthe necessary information as to network health, billing etc. Moreover,IP communication is not based on allocating each “call” with a link offixed bandwidth for the duration of the call: rather bandwidth isallocated by packets on demand, in a link shared with any number ofother data streams.

Accordingly, there is a need for a new kind of monitoring equipmentcapable of grabbing the vast volume of data flowing in the IP networkbearers, and of processing it fast enough to extract and analyse therouting and other information crucial to the monitoring function. Therequirements of extreme reliability mentioned above apply equally in thenew environment.

Networks such as these may be monitored using instruments (generallyreferred to as probes) by making a passive optical connection to theoptical fibre bearer using an optical splitter. However, this approachcannot be considered without due attention to the optical power budgetof the bearer, as the optical splitters are lossy devices. In additionto this, it may be desirable to monitor the same bearer many times or tomonitor the same bearer twice as part of a backup strategy forredundancy purposes. With available instrumentation, this implies amultiplication of the losses, and also disruption to the bearers as eachnew splitter is installed. Issues of upgrading the transmitter and/orreceiver arise as losses mount up.

The inventors have analysed acceSS7 network monitoring systems(unpublished at the present filing date). This shows that the reasonsfor lack of availability of the system can be broken down into threebroad categories: unplanned outages, such as software defects; plannedoutages, such as software and hardware upgrades; and hardware failures.Further analysis shows that the majority of operational hours lost arecaused by planned and unplanned maintenance, while hardware failureshave a relatively minor effect. Accordingly, increasing the redundancyof disk drives, power supplies and the like, although psychologicallycomforting, can do relatively little to improve system availability. Thegreatest scope for reducing operational hours lost and hence increasingavailability is in the category of planned outages.

In order to implement a reliable monitoring system it would therefore beadvantageous to have an architecture with redundancy allowing for spareprobe units that is tolerant of both probe failure and probereconfiguration, and provides software redundancy.

Monitoring equipment designed for this purpose does not currently exist.Service providers may therefore use stand-alone protocol analysers whichare tools really intended for the network commissioning stage. Theseusually terminate the fibre bearer, in place of the product beinginstalled, or they plug into a specific test port on the product

-   -   under test. Specific test software is then needed for each        product. Manufacturers have alternatively built diagnostic        capability into the network equipment itself, but each perceives        the problems differently, leading to a lack of uniformity, and        actual monitoring problems, as opposed to perceived problems,        may not be addressed.

Further considerations include the physical environment needed to housesuch processing architecture. Such a hardware platform should be asflexible as possible to allow for changes in telecommunicationstechnology and utilise standard building blocks to ensure cross platformcompatibility. For example, there exist standards in the USA, as set outby the American National Standards Institute (ANSI) and Bellcore, whichdiffer from those of Europe as set by the European TelecommunicationsStandards Institute (ETSI). Versions of SS7 may also vary from countryto country, owing to the flexibility of the standard, although the ITUstandard is generally used at international gateways. The USA BellcoreNetwork Equipment-Building System (NEBS) is of particular relevance torack-mounted telecommunications equipment as it provides designstandards for engineering construction and should be taken into accountwhen designing network monitoring equipment. Such standards imposelimitations such as connectivity and physical dimensions upon equipmentand, consequently, on cooling requirements and aisle spacing of networkrack equipment.

It is known that standard processing modules conforming for example tothe cPCI standard are suitable for use in telecommunicationapplications. The further standard H. 110 provides a bus formultiplexing baseband telephony signals in the same backplane as thecPCI bus. Even with Intel Pentium™ or similar processors, however, sucharrangements do not currently accommodate the computing power needed forthe capture and analysis of broadband packet data. Examples of protocolsand their data rates to be accommodated in the monitored bearers in thefuture equipment are for example DS3 (44 Mbit.s⁻¹), OC3 (155 Mbit.s⁻¹),OC12 (622 Mbit.s⁻¹) and OC48 (2.4 Gbit.s⁻¹). Aside from the volume ofdata to be handled, conventional chassis for housing such modules do notalso support probe architectures of the type currently desired, both interms of processing capability and also to the extent that theirdimensions do not suit the layout of telecommunication equipment roomssuch as may be designed to NEBS allowing them to co-reside with networkequipment.

For example, the typical general purpose chassis provides a rack-mountedenclosure in which a backplane supports and interconnects a number ofcPCI cards, including a processor card and peripheral cards, to form afunctional system. The cards are generally oriented vertically, withpower supply (PSU) modules located above or below. Fans force airthrough the enclosure from bottom to top for cooling the modules. Aperipheral card may have input and output (I/O) connections on its frontpanel. Alternatively, I/O connections may be arranged at the rear of theenclosure, using a special “transition card”. Examples of rack widths incommon use are 19 inch (483 mm) and 23 inch (584 mm). The siting ofracks in telecommunications equipment rooms implies an enclosure depthshould be little over 12 inches (305 mm). However, cPCI and VME standardprocessor cards and compatible peripheral cards are already 205 mm deep(including mountings) and the conventional interface card mounted behindthe back plane adds another 130 mm. Moreover, although parts of theconnector pin-outs for cPCI products are standardised, different vendorsuse other connectors differently for management bus signals and for LANconnections. These variations must also be adapted to by dedicatedinterconnect, and designs will often assume that cards from a singlevendor only are used.

In a first aspect the invention provides a rack-mountable enclosurecomprising a housing and interconnection backplane for the mounting andinterconnection of a plurality of card-shaped processing modules and atleast one interface module, the interface module being arranged toprovide a plurality of external connectors and to transport signals viathe backplane between each external connection and an individualprocessing module, wherein:

-   -   said backplane provides locations for said processing modules to        lie across a major portion of the backplane area facing a front        side of the enclosure;    -   said backplane provides a location for said interface module        over a minor portion of the backplane area facing a rear side of        the enclosure, so as to provide said external connectors at the        rear of the enclosure; and    -   a power supply module for powering the modules within the        enclosure is positioned over another portion of the backplane        area, on the same side as the interface module.

This arrangement allows a compact housing to contain several processingmodules and to receive a corresponding number of external connections,in a more compact and functionally dense manner than known instrumentchassis designs. In particular, the location of the power supply modulebehind the backplane saves height and/or width in the rack.

It will be understood that “front” and “rear” are used for convenience,and their meanings can be reversed. One particular benefit of thespecified arrangement is that all external connectors (and hence theassociated cabling) can be located on one side of the enclosure,allowing consistent access for all cables at the rear in the crowdedequipment rooms common to telecommunication and other installations.Using cPCI standard processor and peripheral cards, the depth of theenclosure can be kept within or close to 12 inches (305 mm), no greaterthan the surrounding telecommunication equipment.

The enclosure may be constructed so that the processor modules liegenerally horizontally when the enclosure is rack mounted. Air paths maybe defined through the enclosure so as to pass from end to end thereof,along and between the processor modules and, if necessary, the powersupply and interface modules. Fans may be included, optionally in aredundant configuration, to ensure adequate air flow to cool the variouscomponents of the enclosure.

The external connectors may provide inputs, outputs or both. In atelecommunications network probe application, the transport of data inthe backplane will generally be inward, from the external connectors tothe processing modules. In particular, external input connectors may beprovided by the interface module for broadband telecommunicationssignals, with high bandwidth interconnections provided in the backplane.In principle, the backplane could include optical interconnects. Withpresent technology, however, any necessary optical to electricalconversion will more likely be included in the interface module. Inother applications, for example process control or computer telephony,the transport may be in both directions, or outwards only. The transportvia the backplane may be in essentially the same format in which itarrives. Alternatively, the interface module may change the format, forexample to multiplex several of the external signals onto a single pairof conductors in the backplane. The enclosure and modules will findparticular application wherever a large quantity of data needs to beprocessed at speed, and reduced by filtering and aggregation to provideinformation for use elsewhere.

For flexibility and particularly for redundancy in fault and maintenancesituations, the enclosure may provide a location for at least oneswitching module, whereby routing of signals between the externalconnectors and individual processing modules can be varied. Theswitching module may in particular comprise a cross-point switch, inaccordance with another aspect of the invention, set forth in moredetail elsewhere. It is assumed in that case that the processing modulesare “hot-swappable”, so that operation of other modules is unaffected bymodule replacement. The switching module may be operable to routesignals between one external connector and a plurality of processingmodules. This allows increased processing capacity to be provided foreach external connector, whether this is used for redundancy or merelyto add processing functionality.

For additional redundancy in larger systems, the switching module andinterface module may provide for re-routing one of said signals from anexternal input connector to an additional output connector, to allowprocessing in another enclosure. The number of external input connectorsmay exceed the capacity of processing modules that can be accommodated,or may match it.

The backplane may separately provide local bus interconnections forcommunication between the processing modules. Said local businterconnections may include a processor-peripheral parallel bus, forexample cPCI. The processing module locations may be subdivided intogroups, each group receiving a set of separately pluggable modules whichtogether co-operate for processing of a given external signal. Thebackplane may in particular provide a plurality of independent localbuses, each for communication between the modules of one group. Thegroups may each include a first processor module having specificcapability for a type of input signal (such as IP packet data) to beanalysed, and a second processor module of generic type for receivingpartially processed data from the first processor module, and forfurther processing and reducing said data for onward communication.

The first and second processing modules can be regarded as packet andprobe processor modules respectively, each such pair forming aself-contained probe unit. It will be understood that each probeprocessor card may be served by more than one packet processor card, andreferences to pairs should not be construed as excluding the presence ofa further packet processor module in any group.

In the specific embodiments disclosed herein, two separate interfacemodules are provided at the rear side of the backplane. A firstinterface module, being the one referred to above, is for the signals tobe processed (which broadly could mean input signals to be analysed oroutput signals being generated). A second interface module is providedfor communication for control and management purposes, such as theonward communication of the processing results via LAN. These modulescould of course be combined in one physical module, or furthersub-divided, according to design requirements.

The external outputs may be connections to a computer Local Area Network(LAN), which can also provide for remote control and configuration ofthe processing modules. For redundancy of operation, the LAN connectionsin the backplane can be unique to each module, and can further beduplicated for each module. Alternatively, all modules can communicatevia a common LAN. The backplane may provide a dedicated location for amanagement module for selective routing of the LAN or other outputcommunications from the external connectors to the processing modules.

The backplane may further provide a communication bus connecting allmodules, for management functions including for example power andcooling management. Said interconnections may for example include an I²Cor SMB bus carrying standard protocols. For improved redundancy,separate buses may be provided for each sub-system.

Combining the above features, according to a particular embodiment ofthe invention in its first aspect, the backplane may provide:

-   -   a plurality of pairs of processing module locations, each pair        comprising adjacent first and second processing module        locations;    -   a plurality of independent communication buses each extending        between the first processing module location and second        processing module location of a respective one of said pairs;    -   a plurality of independent interconnections each for bringing a        different external input signal from said interface module to a        respective one of said first processing module location;    -   one or a plurality of independent interconnections for bringing        communication signals from said second processing module        locations to a second interface module.

The enclosure and backplane may further provide a location for acommunication and management module to provide one or more of thefollowing functions:

-   -   routing of processing module communication and management        signals;    -   communication (e.g. LAN) switching to route communications from        the processing modules to the outside world with sufficient        redundancy and bandwidth;    -   “magic packet” handling, to allow remote resetting of the        modules within the enclosure; and    -   environmental control, controlling fan speed in response to        operating temperatures sensed on each module.

Alternatively, the first aspect of the invention provides arack-mountable enclosure comprising a housing, a power supply module, afan assembly and an interconnection backplane for the mounting andinterconnection of a plurality of card-shaped processing modules,wherein the processing modules in use are arranged to lie generallyhorizontally in front of the backplane and generally parallel with oneanother, the power supply module is located behind the backplane, andthe fan assembly is located to left or right of the processing modules(in use, as viewed from the front) so as to provide a generallyhorizontal airflow between them.

A shared interface module or modules for providing external connectionsto the backplane and hence to all of the processing modules may also belocated behind the backplane.

It is noted at this point that the cPCI standard defines a number ofphysical connectors to be present on the backplane, but only two ofthese (J1, J2) are specified as to their pin functions. Although thesecond processing modules mentioned above are generic processor cardsbased for example on Pentium (™ of Intel Corp.) microprocessors,different card vendors use the remaining connectors differently forcommunication and management signals such as SMB and LAN connections.

According to a second aspect of the invention a multi-processorequipment enclosure provides a housing and a backplane providinglocations for a plurality of processing modules, and further providing aplurality of locations for a configuration module corresponding torespective processing module locations, each configuration moduleadapting the routing of communication and management signals via thebackplane, in accordance with the vendor-specific implementation of theprocessing module.

The configuration module locations may be on the backplane, or onanother card connected to the backplane. In the preferred embodiment, acommunication and management module is provided at a specific location,and the configuration module locations are provided on the managementmodule.

In an alternative solution according to the second aspect of theinvention, a multi-processor processor equipment enclosure provides ahousing and a backplane providing interconnect for a plurality ofprocessing modules and a management module, the backplane interconnectincluding generic portions standardised over a range of processingmodules and other portions specific to different processing moduleswithin said range, wherein said management module is arranged to senseautomatically the specific type of processing module using protocolsimplemented by the modules via connections in the generic portion of theinterconnect, and to route communication and management signals via thebackplane, in accordance with the specific implementation of eachprocessing module.

The type sensing protocols may for example be implemented via geographicaddress lines in the standardised portion of a compact PCI backplane.

It is noted that known chassis designs and backplanes do not provide forseveral channels of signals to be monitored by independent processingsub-systems within the same chassis, especially when each monitoringunit processor in fact requires more than one card slot for itsimplementation. In particular, for monitoring of broadband communicationsignals in IP or similar protocols, it is presently necessary to providea first processing module dedicated to a first stage of data acquisitionand processing, where the sheer quantity of broadband data would defeata general-purpose processor card, and a second processing module ofgeneric type, for further processing onward reporting of the dataprocessed by the first processing module.

According to a third aspect of the invention a computer equipmentchassis provides a housing and backplane providing locations for atleast four independent processing subsystems, each processing sub-systemcomprising first and second processing modules separately mounted on thebackplane at adjacent locations, wherein the backplane provides at leastfour independent CPU-peripheral interfaces, each extending only betweenthe adjacent locations of said first and second processing modules, thefirst processing module operating as a peripheral and the secondprocessing module operating as host.

The enclosure and backplane may further provide a location for amulti-channel interface module providing external connections for all ofthe processing sub-systems, the backplane routing signals from theinterface module to the appropriate processing sub-systems. Theenclosure and backplane may further provide a location for a switchingmodule, such that each external connection can be routed and re-routedto different processing sub-systems.

The backplane may further provide interconnections between the channelprocessors for communication externally of the enclosure. The enclosureand backplane may further provide a management module location forrouting of said communication from the channel processors to externalconnectors. Said interconnections may form part of a computer local areanetwork (LAN). The enclosure and backplane may in fact provide multipleredundant network connections in order that said onward communicationcan continue in the event of a network outage.

The inventors have recognised that, particularly because passive opticalsplitters have extremely high reliability, a probe architecture whichprovides for replication and redundancy in the monitoring system afterthe splitter would allow all the desired functionality and reliabilityto be achieved, without multiple physical taps in the network bearer,and hence without excessive power loss and degradation in the systembeing monitored.

In a fourth aspect the invention provides a multi-channel networkmonitoring apparatus for the monitoring of traffic in a broadbandtelecommunications network, the apparatus comprising:

-   -   a plurality of external input connectors for receipt of network        signals to be monitored;    -   a plurality of channel processors mounted within a chassis, each        for receiving and processing a respective incoming signal to        produce monitoring results for onward communication, the        incoming network signals individually or in groups forming        channels for the purposes of the monitoring apparatus, each        channel processor being arranged to operate independently of the        others and being replaceable without interrupting their        operation;    -   one or more external communication connectors for onward        communication of said monitoring results from the channel        processors; and    -   a switching unit;    -   wherein the external input connectors are connected to the        channel processors via said switching unit, the switching unit        in use routing each incoming signal to a selected channel        processor and being operable to re-route an incoming channel to        another selected channel processor in the event of processor        outage.

The switching unit may further be operable to connect the same incomingchannel simultaneously to more than one channel processor. The samebearer can therefore be monitored in different ways, without the needfor another physical tap.

The channel processors may be in the form of modules mounted andinterconnected on a common backplane. The switching unit may comprise afurther module mounted on said backplane. The external input connectorsmay be provided by a common interface module separate from or integratedwith the switching unit.

The external communication connectors may be connected to the channelprocessors via a communication management module and via the backplane.The external communication connectors and communication managementmodule may optionally provide for said onward communication to beimplemented over plural independent networks for redundancy. Redundancyof the networks may extend to each channel processor itself providingtwo or more network connections. In the particular embodimentsdescribed, the backplane provides an independent connection between eachrespective channel processor and the communication management module.This provides better redundancy than shared network communication.

The channel processors may each comprise a self-contained sub-system ofhost and peripheral processing modules interconnected via aCPU-peripheral interface in the backplane, the backplane providing aseparate peripheral interface for each channel processor. Theinterconnection may in particular comprise a parallel peripheralinterface such as cPCI.

The backplane and card-like modules may be provided in a singlerack-mountchassis, which may also house a power supply and cooling fans.These may be arranged internally in accordance with the first aspect ofthe invention, as set forth.

The switching unit may be operable to route any incoming signal to anyof the channel processors. The switching unit may further provide forrouting any of the incoming channels to an further external connector,for processing by a channel processor separate from the chassis.

The invention yet further provides a network monitoring system wherein afirst group of multi-channel network monitoring apparatuses according tothe fourth aspect of the invention as set forth above are connected toreceive a plurality of incoming signals, wherein the switching unit ofeach apparatus in the first group provides for routing any of itsincoming channels to a further external connector, the system furthercomprising at least one further multi-channel network monitoringapparatus according to the fourth aspect of the invention as set forthabove, connected to receive incoming channels from said further externalconnectors of the first group of apparatuses, the further apparatusthereby providing back-up in the event of a channel processor failure orreplacement within the first group of apparatuses.

The invention yet further provides a network monitoring system wherein aplurality of multi-channel network monitoring apparatuses according tothe fourth aspect of the invention as set forth above are connected to alarger plurality of incoming channels via multiplexing means, the totalnumber of channel processors within the monitoring apparatuses beinggreater than the number of incoming channels at any given time, suchthat any incoming channel can be routed by the multiplexing means andappropriate switching unit to an idle channel processor of one of themonitoring apparatuses. This allows the system to continue monitoringall channels in the event of failure or replacement of any channelprocessor.

The number of channel processors may be greater than the number ofincoming channels by at least the number of channel processors in eachmonitoring apparatus. This allows the system to continue monitoring allchannels in the event of failure or replacement of one completeapparatus.

The multiplexing means may be formed by optical switches, while theswitching units within each monitoring apparatus operate on signalsafter conversion to electrical form.

Alternatively, the multiplexing means may include electronic switches,while inputs and outputs are converted to-and-from optical form for easeof interconnection between separate enclosures. In principle, theconversion from optical to electrical for could happen at any point,from the network tap point to the processing module itself.

The above systems will typically further comprise one or moremulti-channel optical power splitters, for tapping into active opticalcommunications bearers to obtain the said incoming signals for themonitoring apparatuses. The redundancy and adaptability within themonitoring system reduces the need for multiple monitoring taps,preserving the integrity of the network.

In a fifth aspect the invention provides a multi-channel replicatingdevice for broadband optical signals, the device comprising one or moremodules having:

-   -   a first plurality of input connectors for receiving broadband        optical signals;    -   a larger plurality of output connectors for broadband optical        signals;    -   means for replicating each received broadband optical signal to        a plurality of said output connectors without digital        processing.

Such a device allows multiple monitoring applications to be performed ona network signal with only one optical tap being inserted in thephysical bearer or the operating network. Redundancy in the monitoringequipment can be provided, also with the single bearer tap. Change inthe configuration of the monitoring equipment can be implemented withoutdisturbing the bearer operation, or even the other monitoringapplications.

The replicating means may in particular involve components for opticalto electrical conversion and back to optical again.

The replicating device may further comprise an one or more additionaloptical outputs, and a selector devices for selecting which of the inputsignals is replicated at said additional output. This selection can beuseful in particular in response to fault situations and planned outageswithin the network monitoring equipment.

The invention in the fifth aspect further provides a telecommunicationsnetwork monitoring system comprising:

-   -   an optical splitting device, providing a tap signal for        monitoring signals carried by a bearer in a broadband        telecommunications network;    -   a plurality of network monitoring units, each for receiving and        analysing signals from a broadband optical bearer; and    -   a signal replicating device according to the fifth aspect of the        invention as set forth above, the signal replicating device        being connected so as to receive said optical tap signal, and to        provide replicas of said optical tap signal to inputs of two or        more of said network monitoring units.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 shows a model of a typical ATM network.

FIG. 2 shows a data collection and packet processing apparatus connectedto a physical telecommunications network via a LAN/WAN interconnect.

FIG. 3 shows the basic functional architecture of a novel network probeapparatus, as featured in FIG. 2.

FIG. 4 shows a simple network monitoring system which can be implementedusing the apparatus of the type shown in FIG. 3.

FIG. 5 shows another application of the apparatus of FIG. 4 giving 3+1redundancy.

FIG. 6 shows a larger redundant network monitoring system including abackup apparatus.

FIG. 7 shows an example of a modified probe apparatus permitting a“daisy chain” configuration to provide extra redundancy and/orprocessing power.

FIG. 8 shows an example of daisy chaining the probe chassis of FIG. 7giving 8+1 redundancy.

FIG. 9 shows a further application of the probe apparatus giving addedprocessing power per bearer.

FIG. 10 shows a second means of increasing processing power by linkingmore than one chassis together.

FIG. 11 shows a signal replicating device (referred to as a BroadbandBridging Isolator (BBI)) for use in a network monitoring system.

FIG. 12 shows a typical configuration of a network monitoring systemusing the BBI of FIG. 11 and several probe apparatuses.

FIGS. 13A and 13B illustrate a process of upgrading the processing powerof a network monitoring system without interrupting operation.

FIG. 14 is a functional schematic diagram of a generalised network probeapparatus showing the functional relationships between the major modulesof the apparatus.

FIG. 15A shows the general physical layout of modules in a specificnetwork probe apparatus implemented in a novel chassis and backplane.

FIG. 15B is a front view of the chassis and backplane of FIG. 15A withall modules removed, showing the general layout of connectors andinterconnections in the backplane.

FIG. 15C is a rear view of the chassis and backplane of FIG. 15A withall modules removed, showing the general layout of connectors andinterconnections in the backplane, and showing in cut-away form thelocation of a power supply module.

FIG. 16 shows in block schematic form the interconnections betweenmodules in the apparatus of FIGS. 15A-C.

FIG. 17 is a block diagram showing in more detail a cross-point switchmodule in the apparatus of FIG. 16, and its interconnections with othermodules.

FIG. 18 is a block diagram showing in more detail a packet processormodule in the apparatus of FIG. 16, and its interconnections with othermodules.

FIG. 19 is a block diagram showing in more detail a combined LAN andchassis management card in the apparatus of FIG. 16.

DETAILED DESCRIPTION OF THE EMBODIMENTS Background

FIG. 1 shows a model of a telecommunication network 10 based onasynchronous transfer mode (ATM) bearers. Possible monitoring points onvarious bearers in the network are shown at 20 and elsewhere. Eachbearer is generally an optical fibre carrying packetised data with bothrouting information and data “payload” travelling in the same datastream. Here “bearer” is used to mean the physical media that carriesthe data and is distinct from a “link”, which in this context is definedto mean a logical stream of data. Many links of data may be multiplexedonto a single bearer. These definitions are provided for consistency inthe present description, however, and should not be taken to imply anylimitation of the applicability of the techniques disclosed, or on thescope of the invention defined in the appended claims. Those skilled inthe art will sometimes use the term “channel” to refer to a link (asdefined), or “channel” may be used to refer to one of a number ofvirtual channels being carried over one link, which comprises thelogical connection between two subscribers, or between a subscriber anda service provider. Note that such “channels” within the largertelecommunications network should not be confused with the monitoringchannels within the network probe apparatus of the embodiments to bedescribed hereinafter.

The payload may comprise voice traffic and/or other data. Differentprotocols may be catered for, with examples showing connections to FreeRelay Gateway, ATM and DSLAM equipment being illustrated. User-Networktraffic 22 and Network—Network traffic 24 are shown here as dashed linesand solid lines respectively.

In FIG. 2 various elements 25-60 of a data collection and packetprocessing system distributed at different sites are provided formonitoring bearers L1-L8 etc. of a telecommunications network. Thebearers in the examples herein operate in pairs L1, L2 etc. forbi-directional traffic, but this is not universal, nor is it essentialto the invention. Each pair is conveniently monitored by a separateprobe unit 25, by means of optical splitters S1, S2 etc. inserted in thephysical bearers. For example, one probe unit 25, which monitors bearersL1 and L2, is connected to a local area network (LAN) 60, along withother units at the same site. The probe unit 25 on an ATM/IP networkmust examine a vast quantity of data, and can be programmed to filterthe data by a Virtual Channel (VC) as a means of reducing the onboardprocessing load. Filtering by IP address can be used to the same effectin the case of IP over SDH and other such optical networks. Similartechniques can be used for other protocols. Site processors 40 collateand aggregate the large quantity of information gathered by the probeunits, and pass the results via a Wide Area Network (WAN) 30 to acentral site 65. Here this information may be used for network planningand operations. It may alternatively be used for billing according tothe volume of monitored traffic per subscriber or service provider orother applications.

The term “probe unit” is used herein refer to a functionallyself-contained sub-system designed to carry out the required analysisfor a bearer, or for a pair or larger group of bearers. Each probe unitmay include separate modules to carry out such operations as filteringthe packets of interest and then interpreting the actual packet or otherdata analysis.

In accordance with current trends, it is assumed in this descriptionthat the links to be monitored carry Internet Protocol (IP) traffic overpassive optical networks (PONS) comprising optical fibre bearers.Connection to such a network can only really be achieved through use ofpassive optical splitters S1, S2 etc. Passive splitters have advantagessuch as high reliability, comparatively small dimensions, variousconnection configurations and the fact that no power or elementmanagement resources required. An optical splitter in such a situationworks by paring off a percentage of the optical power in a bearer to atest port, the percentage being variable according to hardwarespecifications.

A number of issues are raised when insertion of such a device isconsidered. For example, there should be sufficient bearer receiverpower margins remaining at both test device and the through port to therest of the network. It becomes necessary to consider what is the mosteconomic method of monitoring the bearer in the presence of a reducedtest port power budget while limiting the optical power needed by themonitoring probe and if the network would have to be re-configured as aresult of inserting the device.

Consequently, inserting a power splitter to monitor a network frequentlyrequires an increase in launch power. This entails upgrading thetransmit laser assembly and installing an optical attenuator whereneeded to reduce optical power into the through path to normal levels.Such an upgrade would ideally only be performed once.

For these reasons it is not desirable to probe, for example, an ATMnetwork more than once on any given bearer. Nevertheless, it would bedesirable to have the ability for multiple probing devices to beconnected to the same bearer, that is, have multiple outputs from theoptical interface. The different probes may be monitoring differentparameters. In addition, however, any network monitoring system mustoffer a high degree of availability, and multiple probes are desirablein the interests of redundancy. The probe apparatuses and ancillaryequipment described below allow the implementation of such a networkmonitoring system which can be maintained and expanded with simpleprocedures, with minimal disruption to the network itself and to themonitoring applications.

Network Probe System—General Architecture

FIG. 3 shows the basic functional architecture of a multi-channeloptical fibre telecommunications probe apparatus 50 combining severalindividual probe units, into a more flexible system than has hithertobeen available. The network monitoring apparatus shown receives N bearersignals 70 such as may be available from N optical fibre splitters.These enter a cross-point switch 80 capable of routing each signal toany of M individual and independently-replaceable probe units 90. Eachprobe unit corresponds in functionality broadly with the unit 25 shownin FIG. 2. An additional external output 85 from the cross-point switch80 is routed to an external connector. This brings important benefits,as will described below.

The cross-point switch 80 and interconnections shown in FIG. 3 may beimplemented using different technologies, for example using passiveoptical or optoelectronic cross-points. High speed networks, for exampleOC48, require electrical path lengths as short as possible. An opticalswitch would therefore be desirable, deferring as much as possible theconversion to electrical. However, the optical switching technology isnot yet fully mature. Therefore the present proposal is to have anelectrical implementation for the cross-point switch 80, the signalsconverted from optical to electrical at the point of entry into theprobe apparatus 50. The scale of an optoelectronic installation will belimited by the complexities of the cross-point switch and size of theprobe unit. The choice of interconnect technology (for example betweenelectrical and optical), is generally dependent on signalbandwidth-distance product. For example, in the case of highbandwidth/speed standards such as OC3, OC12, or OC48, inter-rackconnections may be best implemented using optical technology.

Detailed implementation of the probe apparatus in a specific embodimentwill be described in more detail with reference to FIGS. 14 to 19. Aspart of this, a novel chassis arrangement for multi-channel processingproducts is described, with reference to FIGS. 15A-15C, which may findapplication in fields beyond telecommunications monitoring. First,however, applications of the multi-channel probe architecture will bedescribed, with reference to FIGS. 4 to 13.

FIG. 4 shows a simple monitoring application which can be implementedusing the apparatus of the type shown in FIG. 3. The cross-point switch80 is integrated into the probe chassis 100 together with up to fourindependently operating probe units. In this implementation of thearchitecture each probe unit (90 in FIG. 3) is formed by a packetprocessor module 150 and single board computer SBC 160 as previouslydescribed. There are provided two packet processors 150 in each probeunit 90. Each packet processor can receive and process the signal of onehalf-duplex bearer. SBC 160 in each probe unit has the capacity toanalyse and report the data collected by the two packet processors.Other modules included in the chassis provide LAN interconnections foronward reporting of results, probe management, power supply, and coolingmodules (not shown in FIGS. 4 to 13B).

In this application example a single, fully loaded chassis 100 is usedwith no redundancy to monitor eight single (four duplex) bearersconnected at 140 to the external optical inputs of the apparatus (inputs70-1 to 70-N in FIG. 3). The cross-point switch external outputs 85 areshown but not used in this configuration. Applications of these outputsare explained for example in the description of FIGS. 6, 8, 10 and 12below.

FIG. 5 shows an alternative application of the apparatus giving 3+1redundancy. Here three duplex bearer signals are applied to externalinputs 140 of the probe apparatus chassis 100, while the fourth pair ofinputs 142 is unused. Within the chassis there are thus three primaryprobe units 90 plus a fourth, spare probe unit 120. The cross-pointswitch 80 can be used to switch any of the other bearers to this spareprobe unit in the event of a failure in another probe unit. Already byintegrating the cross-point switch and several probe units in a singlechassis, a scaleable packet processor redundancy down to 1:1 is achievedwithout the overhead associated with an external cross-point switch.Since electrical failures cause only a very minor proportion of outages,redundancy within the chassis is valuable, with the added bonus thatcomplex wiring outside the chassis may be avoided. One or moreprocessors within each chassis can be spare at a given time, andswitched instantaneously and/or remotely if one of the other probe unitsbecomes inoperative.

FIG. 6 shows a larger redundant system comprising four primary probeapparatuses (chassis 100-1 to 100-4), and a backup chassis 130 whichoperates in the event of a failure in one of the primary chassis. Inthis example of a large redundant system there are 16 duplex bearersbeing monitored. Each external input pair of the backup chassis isconnected to receive a duplex bearer signal from the external opticaloutput 85 of a respective one of the primary apparatuses 100-1 to 100-4.By this arrangement, in the event of a single probe unit failure in oneof the primary apparatuses, a spare probe unit within the backup chassiscan take over the out-of-service unit's function. Assuming all inputsand all of the primary probe units are operational in normalcircumstances, we may say that 4:1 redundancy is provided.

Recognising that in this embodiment only one optical interface isconnected to the bearer under test, the chassis containing the opticalinterfaces can if desired have redundant communications and/or powersupply units (PSUs) and adopt a “hot swap” strategy to permit rapidreplacement of any hardware failures. “Hot swap” in this context meansthe facility to unplug one module of a probe unit within the apparatusand replace it with another without interrupting the operation orfunctionality of the other probe units. Higher levels of protection canbe provided on top of this, if desired, as described below withreference to FIGS. 15A-C and 16.

FIG. 7 shows a modified probe apparatus which provides an additionaloptical input 170 to the cross-point switch 80. In other words, thecross-point switch 80 has inputs for more bearer signals than can bemonitored by the probe units within its chassis. At the same time, withthe external optical outputs 85, the cross-point switch 80 outputs formore signals than can be monitored by the probe units within thechassis. These additional inputs 170 and outputs 85 can be used toconnect a number of probe chassis together in a “daisy chain”, toprovide extra redundancy and/or processing power. By default, in thepresent embodiment, copies of the bearer signals received at daisy chaininputs 170 are routed to the external outputs 85. Any other routing canbe commanded, however, either from within the apparatus or from outsidevia the LAN (not shown).

FIG. 8 shows an example of daisy chaining the probe chassis to give 8:1redundancy.

The four primary probe chassis 100-1 to 100-4 are connected in pairs(100-1 & 100-2 and 100-3 & 100-4). The external outputs 85 on the firstchassis of each pair are connected to the daisy chain inputs 170 on thesecond chassis. The external outputs 85 of the second chassis areconnected to input of a spare of backup chassis 130 as before. Theseconnections can carry the signal through to the spare chassis when therehas been a failure in a probe unit in either the first or second chassisin each pair. Unlike the arrangement of FIG. 6, however, it will be seenthat the backup chassis 130 still has two spare pairs of externalinputs. Accordingly, the system could be extended to accommodate afurther four chassis (up to sixteen further probe units, and up tothirty-two further bearer signals), with the single backup chassis 130providing some redundancy for all of them.

For applications that involve processor intensive tasks it may bedesirable to increase the processing power available to monitor eachbearer. This may be achieved by various different configurations, andthe degree of redundancy can be varied at the same time to suit eachapplication.

FIG. 9 illustrates how it is possible to increase the processing poweravailable for any given bearer by reconfiguring the probe units. In thisconfiguration only two duplex bearer signals 140 are connected to thechassis 100. Two inputs 142 are unused. Within the cross-point switch 80each bearer signal is duplicated and routed to two probe units 90. Thisdoubles the processing power available for each of the bearers 140. Thismay be for different applications (for example routine billing and frauddetection), or for more complex analysis on the same application. Eachpacket processor (150, FIG. 4) and SBC (160) will be programmedaccording to the application desired. In particular, each packetprocessor, while receiving and processing all the data carried by anassociated bearer, will be programmed to filter the data and to pass ononly those packets, cells, or header information which is needed by theSBC for a particular monitoring task. The ability to provide redundancyvia the external outputs 85 still remains.

FIG. 10 illustrates a second method of increasing processing power is byconnecting more than one chassis together in a daisy chain or similararrangement. Concerning the “daisy chain” inputs, FIG. 10 alsoillustrates how a similar effect can be achieved using the unmodifiedapparatus (FIG. 3), providing the apparatus is not monitoring its fullcomplement of bearer signals. The external inputs can thus be connectedto the external outputs 85 of the previous chassis, instead of usingspecial inputs 170 as shown in FIGS. 7 and 8.

In the configuration of FIG. 10, two chassis 100-1 and 100-2 are fullyloaded with four probe units 90 each. External signals for all eightprobe units are received at 140 from a single duplex bearer. Thecross-point switch 80 is used to replicate these signals to every probeunit 90 within the chassis 100-1, and also to the external outputs 85 ofthe first chassis 100-1. These outputs in turn are connected to one pairof inputs 144 of the second chassis 100-2. Within the second chassis,the same signals are replicated again and applied to all four probeunits, and (optionally) to the external outputs 85 of the second chassis100-2.

Thus, all eight probe units are able to apply their processing power tothe same pair of signals, without tapping into the bearer more thanonce. By adding further chassis in such a daisy chain, processing poweris scaleable practically to as much processing power as needed.

The examples given are for way of illustration only, showing how usingthe chassis architecture described it is possible to provide the userwith the processing power needed and the redundancy to maintainoperation of the of the system in the event of faults and plannedoutages. It will be appreciated that there are numerous differentconfigurations possible, besides those described.

For example, it is also possible to envisage a bi-directional daisychain arrangement. Here, one output 85 of a first chassis might beconnected to one input 170 of a second chassis, while the other output85 is connected to an input 170 of a third chassis. This arrangement canbe repeated if desired to form a bi-directional ring of apparatuses,forming a kind of “optical bus”.

The probe apparatus described above allow the system designer to achieveN+1 redundancy by using the cross-point switch 80 to internally re-routea bearer to a spare processor, or to another chassis. On the other hand,it will be recognised that some types of failure (e.g. in the chassispower supply) will disrupt operation of all of the processors in thechassis. It is possible to reduce such a risk by providing N+1 PSUredundancy, as will be/has been described.

Broadband Bridging Isolator

FIG. 11 shows an optional signal replicating device for use inconjunction with the probe apparatus described above, or othermonitoring apparatus. This device will be referred to as a BroadbandBridging Isolator (BBI). Broadband Bridging Isolator can be scaled todifferent capacities, and to provide additional fault toleranceindependently of the probe apparatuses described above. The basic unitcomprises a signal replicatorl75. For each unit, an (optical) input 176is converted at 177 to an electrical signal, which is then replicatedand converted at 179 etc. to produce a number of identical opticaloutput signals at outputs 178-1 etc.

Also provided within BBI 172 are one or more standby selectors(multiplexers) 180 (one only shown). Each selector 180 receives replicasof the input signals and can select from these a desired one to bereplicated at a selector optical output 182. An additional input 186(shown in broken lines) may be provided which passes to the selector 180without being replicated, to permit “daisy chain” connection.

In use, BBI 172 takes a single tap input 176 from a bearer beingmonitored and distributes this to multiple monitoring devices, forexample probe apparatuses of the type shown in FIGS. 3 to 10. Forreliability, the standby selector 180 allows any of the input signals tobe switched to a standby chassis.

The number of outputs that are duplicated from each input is notcritical. A typical implementation may provide four, eight or sixteenreplicators 175 in a relatively small rack mountable chassis, eachhaving (for example) four outputs per input. Although the concepts hereare described in terms of optical bearers, the same concepts could beapplied to high speed electrical bearers (e.g. E3, DS3 and STM1e).

The reasons for distributing the signal could be for multipleapplications, duplication for reliability, load sharing or a combinationof all three. It is important that only one tap need be made in theoperational bearer. As described in the introductory part of thisspecification, each optical tap reduces the strength of the opticalsignal reaching the receiver. In marginal conditions, adding a tap mayrequire boosting the signal on the operational bearer. Network operatorsdo not want to disrupt their operational networks unless they have to.The BBI allows different monitoring apparatuses for differentapplications to be connected, and removed and re-configured withoutaffecting the operational bearer, hence the name “isolator”. The BBI caneven be used to re-generate this signal by feeding one of the outputsback into the network, so that the BBI becomes part of the operationalnetwork.

The number of bearer signals that are switched through the standbyselector 180 will depend on the users requirements—this numbercorresponds effectively to “N” in the phrase “N+1 redundancy”. Thenumber of standby selectors in each BBI is not critical. Adding moremeans that more bearers can be switched should there be a failure.

The BBI must have high reliability as when operational in a monitoringenvironment it an essential component in the monitoring of data,providing the only bridging link between the signal bearers and theprobe chassis. No digital processing of the bearer signal is performedin the BBI, which can thus be made entirely of the simplest and mostreliable optoelectronic components. When technology permits, in terms ofcost and reliability, there may be an “all-optical” solution, whichavoids conversion to electrical form and back to optical. Presently,however, the state of the art favours the optoelectronic solutiondetailed here. The BBI can be powered from a redundant power supply toensure continuous operation. The number of bearers handled on a singlecard can be kept small so that in event of a failure the number ofbearers impacted is small. The control of the standby switch can be byan external control processor.

FIG. 12 shows a system configuration using BBIs and two separate probechassis 100-1 and 100-2 implementing separate monitoring applications.The two application chassis may be operated by different departmentswithin the network operators organisation. A third, spare probe chassis130 is shared in a standby mode. This example uses two BBIs 172 tomonitor a duplex bearer pair shown at L1, L2, and other bearers notshown. Splitters S1 and S2 respectively provide tap input signals fromL1, L2 to the inputs 176 of the separate BBIs. Each BBI duplicates thesignal at its input 176 to two outputs 178, and the manner describedabove with reference to FIG. 11. For improved fault tolerance, the twofour-way BBIs 172 are used to half duplex bearers L1 and L2 separately.In other words, the two halves of the same duplex bearer are handled bydifferent BBIs. Three further duplex bearers (L3-L8, say, not shown inthe drawing), are connected to the remaining inputs of the BBIs 172 in asimilar fashion.

Using the standby selector 180 any one of the bearers can be switchedthrough to the standby chassis 130 in the event of a failure of a probeunit in one of the main probe chassis 100-1, 100-2. It will beappreciated that, if there is a failure of a complete probe chassis,then only one of the bearers can be switched through to the standbyprobe. In a larger system with, say, 16 duplex bearers, four main probechassis and two standby chassis, the bearers distributed by each BBI canbe shared around the probe chassis so that each probe chassis processesone bearer from each BBI. Then all four bearers can be switched to thestandby probe in the event of a complete chassis failure.

It will be seen that the BBI offers increased resilience for usersparticularly when they have multiple departments wanting to look at thesame bearers. The size of the BBI used is not critical and practicalconsiderations will influence the number of inputs and outputs. Forexample, the BBI could provide inputs for 16 duplex bearers, each beingdistributed to two or three outputs with four standby outputs. Wheremultiple standby circuits are used each will be capable of beingindependently switched to any of the inputs.

FIGS. 13A and 13B illustrate a process of upgrading the processing powerof a network monitoring system without interrupting operation, using thefacilities of the replicating devices (BBIs 172) and probe chassisdescribed above. FIG. 13A shows an example of an “existing” system withone probe chassis 100-1. Four duplex bearer signals are applied toinputs 140 of the chassis. Via the internal cross-point switch 80, eachbearer signal is routed to one probe unit 90. With a view to furtherupgrades and fault tolerance, a broadband bridging isolator (BBI). Eachbearer signal is received from a tap in the actual bearer (not shown) ata BBI input 176. The same bearer signal is replicated at BBI outputs178-1, 178-2 etc. The first set of outputs 178-1 are connected to theinputs 140 of the probe chassis. The second set of outputs 178-2 are notused in the initial configuration.

FIG. 13B shows the an expanded system, which includes a second probechassis 100-2 also loaded with four probe units 90. Consequently thereare now provided two probe units per bearer, increasing the processingpower available per bearer. It is a simple task to migrate from theoriginal configuration in FIG. 13A to the new one shown in FIG. 13B:

-   -   Step 1 —Install the extra chassis 100-2 with the probe units,        establishing the appropriate power supply and LAN        communications.    -   Step 2—Connect two of the duplicate BBI outputs 186 to inputs of        the extra chassis 100-2. (All four could be connected for        redundancy if desired.)    -   Step 3—Configure the new chassis 100-2 and probe units to        monitor the two bearer signals in accordance with the desired        applications.    -   Step 4—Re-configure the original chassis to cease monitoring the        corresponding two bearer signals of the first set of outputs        178-1 (188 in FIG. 13B). (The processing capacity freed in the        original chassis 100-1 can then be assigned expanded monitoring        of the two duplex bearer signals which remain connected to the        BBI outputs 178-1.)    -   Step 5—Remove the connections 188 no longer being used. (These        connections could be left for redundancy if desired.)

In this example the processing power has been doubled from one probeunit per bearer to two probe units per bearer but it can be seen thatsuch a scheme could be easily extended by connecting further chassis. Atno point has the original monitoring capacity been lost, and at no pointhave the bearers themselves (not shown) been disrupted. Thus, forexample, a module of one probe unit can be removed for upgrade whileother units continue their own operations. If there is spare capacity,one of the other units can step in to provide the functionality of theunit being replaced. After Step 2, the entire first chassis 100-1 couldbe removed and replaced while the second chassis 100-2 steps in toperform its functions. Variations on this method are practicallyinfinite, and can also be used for other types of migration, such aswhen increasing system reliability.

The hardware and methods used in these steps can be arranged to complywith “hot-swap” standards as defined earlier. The system of FIGS. 13Aand 13B, and of course any of the systems described above, may furtherprovide automatic sensing of the removal (or failure) of a probe unit(or entire chassis), and automatic re-configuration of switches andre-programming of probe units to resume critical monitoring functionswith minimum delay. Preferably, of course, the engineer would instructthe re-programming prior to any planned removal of a probe unit module.A further level of protection, which allows completely uninterruptedoperation with minimum staff involvement, is to sense the unlocking of aprocessing card prior to actual removal, to reconfigure other units totake over the functions of the affected module, and then to signal tothe engineer that actual removal is permitted. This will be illustratedfurther below with reference to FIG. 15A.

Multi-Channel Probe Apparatus—Functional Arrangement

FIG. 14 is a functional block schematic diagram of a multi-channel probeapparatus suitable for implementing the systems shown in FIGS. 4 to 13Aand 13B. Like numerals depict like elements. All of the modules shown inFIG. 14 and their interconnections are ideally separately replaceable,and housed within a self-contained enclosure of standard rack-mountdimensions. The actual physical configuration of the network probe unitmodules in a chassis with special backplane will be described later.

A network interface module 200 provides optical fibre connectors for theincoming bearer signals EXT 1-8 (70-1 to 70-N in FIG. 3), and performsoptical to electrical conversion. A cross-point switch 80 provides ameans of linking these connections to appropriate probe units 90. Eachinput of a probe unit can be regarded as a separate monitoring channelCH1, CH2 etc. As mentioned previously, each probe unit may in factaccept plural signals for processing simultaneously, and these may ormay not be selectable independently, or grouped into larger monitoringchannels. Additional optical outputs EXT 9,10 are provided to act as“spare” outputs (corresponding to 85 in FIG. 4)In the embodiment, eachprobe unit 90 controls the cross-point switch 80 to feed its inputs(forming channel CH1, 2, 3 or 4 etc.) with a bearer signal selected fromamong the incoming signals EXT 1-8. This selection may be pre-programmedin the apparatus, or may be set by remote command over a LAN. Each probeunit (90) is implemented in two parts, which may conveniently berealised as a specialised packet processor 150 and a general purposesingle board computer SBC 160 module. There are provided four packetprocessors 150 to 150 each capable of filtering and pre-processing eighthalf duplex bearer signals at full rate, and four SBCs 160 capable offurther processing the results obtained by the packet processors. Thepacket processors 150 comprise dedicated data processing hardware, whilethe SBC can be implemented using industry standard processors or othergeneral purpose processing modules. The packet processors 150 areclosely coupled by individual peripheral buses to their respective SBCs160 so as to form self-contained processing systems, each packetprocessor acting as a peripheral to its “host” SBC. Each PacketProcessor150 carries out a high speed time critical cell and packetprocessing including data aggregation and filtering. A second level ofaggregation is carried out in the SBC 160.

LAN and chassis management modules 230, 235 (which in the implementationdescribed later are combined on a single card) provide central hardwareplatform management and onward communication of the processing results.For this onward communication, multiple redundant LAN interfaces areprovided between every SBC 160 and the LAN management module 230 acrossthe backplane. The LAN management function has four LAN inputs (one fromeach SBC) and four LAN outputs (for redundancy) to the monitoring LANnetwork. Multiple connections are provided as different SBCmanufacturers use different pin connectors on their connectors. For anyparticular manufacturer there is normally only one connection betweenthe SBC 160 and the LAN management module 230. The dual redundant LANinterfaces are provided for reliability in reporting the filtered andprocessed data to the next level of aggregation (site processor 40 inFIG. 2). This next level can be located remotely. Each outgoing LANinterface is connectable to a completely independent network, LANA orLANB to ensure reporting in case of LAN outages. In case of dualoutages, the apparatus has buffer space for a substantial quantity ofreporting data.

The chassis management module 235 oversees monitoring and wiringfunctions via (for example) an I²C bus using various protocols. AlthoughI²C is normally defined as a shared bus system, each probe unit forreliability has its own I²C connection direct to the management module.The management module can also instruct the cross-point switch toactivate the “spare” output (labelled as monitoring channels CH9,10 andoptical outputs EXT 9,10) when it detects failure of one of the probeunit modules. This operation can also be carried out under instructionvia LAN.

The network probe having the architecture described above must berealised in a physical environment capable of fulfilling the functionalspecifications and other hardware platform considerations such as thetelecommunications environment it is to be deployed in. A novel chassis(or “cardcage”) configuration has been developed to meet theserequirements within a compact rack-mountable enclosure. The chassis isdeployed as a fundamental component of the data collection andprocessing system.

Multi-Channel Probe Apparatus—Physical Implementation

FIGS. 15A, B and C show how the probe architecture of FIG. 14 can beimplemented with a novel chassis, in a particularly compact and reliablemanner. To support the network probe architecture for this embodimentthere is also provided a custom backplane 190. FIG. 16 shows whichsignals are carried by the backplane, and which modules provide theexternal connections. Similar reference signs are used as in FIG. 14,where possible.

Referring to FIG. 16 for an overview of the functional architecture, thesimilarities with the architecture of FIG. 14 will be apparent. Thenetwork probe apparatus again has eight external optical terminals forsignals EXT 1-8 to be monitored. These are received at a networkinterface module 200. A cross-point switch module 80 receives eightcorresponding electrical signals EXT 1′-8′ from module 200 through thebackplane 190. Switch 80 has ten signal outputs, forming eightmonitoring channels CH1-8 plus two external outputs (CH9,10). Fourpacket processor modules 150-1 to 150-4 receive pairs of these channelsCH 1,2, CH3,4 etc. respectively. CH9,10 signals are fed back to thenetwork interface module 200, and reproduced in optical form at externalterminals EXT 9,10. All internal connections just mentioned are madethrough the backplane via transmission lines in the backplane 190. Eachpacket processor is paired with a respective SBC 160-1 to 1604 byindividual cPCI bus connections in the backplane.

A LAN & Chassis Management module 230 is provided, which is connected tothe other modules by I²C buses in the backplane, and by LAN connections.A LAN interface module 270 provides external LAN connections for theonward reporting of processing results. Also provided is a fan assembly400 for cooling and a power supply (PSU) module 420.

Referring to the views in FIG. 15A chassis 100 carries a backplane 190and provides support and interconnections for various processingmodules. Conventionally, the processing modules are arranged in slots tothe “front” of the backplane, and space behind the backplane in atelecommunications application is occupied by specialised interconnect.This specialised interconnect may include further removable I/O cardsreferred to as “transition cards”. The power supply and fans aregenerally located above and/or below the main card space, and the cards(processing modules) are arranged vertically in a vertical airflow.These factors make for a very tall enclosure, and one which is fardeeper than the ideals of 300 mm or so in the NEBS environment. Thepresent chassis features significant departures from the conventionaldesign, which result in a compact and particularly shallow enclosure.

In the present chassis, the power supply module (PSU) 420 is located ina shallow space behind the backplane 190. The processing modules 150-1,160-1 etc. at the front of the backplane are, moreover, arranged to liehorizontally, with their long axes parallel to the front panel. Thecooling fans 400 are placed to one side of the chassis. Airflow entersthe chassis at the front at 410 and flows horizontally over thecomponents to be cooled, before exiting at the rear at 412. Thisarrangement gives the chassis a high cooling capability while at thesame time not extending the size of the chassis beyond the desireddimensions. The outer dimensions and front flange of the housing allowthe chassis to be mounted on a standard 19 inch (483 mm) equipment rack,with just 5 U height. Since the width of the enclosure is fixed bystandard rack dimensions, but the height is freely selectable, thehorizontal arrangement allows the space occupied by the enclosure to bematched to the number of processor slots required by the application. Inthe known vertical orientation, a chassis which provides ten slots mustbe just as high as one which provides twenty slots, and additionalheight must be allowed for airflow arrangements at top and bottom.

Referring also to FIGS. 15B and 15C, there are ten card slots labelledF1-F10 on the front side of the backplane 190. There are two shallowslots B1 and B2 to the rear of the backplane 190, back-to back with F9and F10 respectively. The front slot dimensions correspond to those ofthe cPCI standard, which also defines up to five standard electricalconnectors referred to generally as J1 to J5, as marked in FIGS. 15B and15C. It will be known to the skilled reader that connectors J1 and J2have 110 pins each, and the functions of these are specified in the cPCIstandard (version PICMG 2.0 R2.1 (May 1st 1998)).

Other connector positions are used differently by differentmanufacturers.

Eight of the front slots (F1-F8) support the Packet Processor/SBC cardsin pairs. The cards are removable using ‘hot swap’ techniques, aspreviously outlined, using thumb levers 195 to lock/unlock the cards andto signal that a card is to be inserted/removed. The other two frontslots F9 and F10 are used for cross-point switch 80 and LAN/Managementcard 230 respectively. Slots F1 to F8 comply with the cPCI insofar asconnectors J1, J2, J3 and J5 are concerned. Other bus standards such asVME could be also be used. The other slots F9 and F10 are unique to thisdesign. All of the cPCI connections are standard and the connectivity,routing and termination requirements are taken from the cPCI standardspecification. Keying requirements are also taken from the cPCIstandard. The cPCI bus does not connect all modules, however: it issplit into four independent buses CPCI1-4 to form four self-containedhost-peripheral processing sub-systems. Failure of any packetprocessor/SBC combination will not affect the other three probe units.

Each of the cards is hot-swappable and will automatically recover fromany reconfiguration. Moreover, by providing switches responsive tooperation of the thumb leversl95, prior to physical removal of the card,the system can be warned of impending removal of an module. This warningcan be used to trigger automatic re-routing of the affected monitoringchannel(s). The engineer replacing the card can be instructed to await avisual signal on the front panel of the card or elsewhere, beforecompleting the removal of the card. This signal can be sent by theLAN/Management module 270, or by a remote controlling site. This schemeallows easy operation for the engineer, without any interruption of themonitoring functions, and without special steps to command there-routing. Such commands might otherwise require the co-ordination ofactions at the local site with staff at a central site, or at best thesame engineer might be required to move between the chassis being workedupon and a nearby PC workstation.

As mentioned above, the upper two front slots (F10, F9) hold the LAN &Management module 230 and the cross-point switch 80 respectively. SlotB1 (behind F9) carries a Network Transition card forming networkinterface module 200, while the LAN interface 270 in slot B2 (behindF10) carries the LAN connectors. All external connections are to theapparatus are provided by special transition cards in these rear slots,and routed through the backplane. No cabling needs to reach directly therear of the individual probe unit slots. No cabling at all is requiredto the front of the enclosure. This is not only tidy externally of thehousing, but leaves a clear volume behind the backplane which can beoccupied by the PSU 420, shown cut-away in FIG. 15C, yielding asubstantial space saving over conventional designs and giving greaterease of maintenance. The rear slot positions B1, B2 are slightly wider,to accommodate the PSU connectors 422.

The J4 position in the backplane is customised to route high integritynetwork signals (labelled “RF” in FIG. 15B). These are transported oncustom connections not within cPCI standards. FIG. 15B showsschematically how these connectors transport the bearer signals inmonitoring channels CH1 etc. from the cross-point switch 80 in slot F9to the appropriate packet processors 150-1 etc. in slots F2, F4, F6, F8.The external bearer signals EXT1′-8′ in electrical form can be seenpassing through the backplane from the cross-point switch 80 (in slotF9) to the network interface module 200 (B1). These high speed,high-integrity signals are carried via appropriately designedtransmission lines in the printed wiring of the backplane 190. Thevariation in transmission delay between channels in the chassis is notsignificant for the applications envisaged. However, in order to avoidphase errors it is still important to ensure that each half of anydifferential signal is routed from its source to its destination usingessentially equal delays. To ensure this, the delays must be matched tothe packet processors for each set for the backplane and cross-pointswitch combination.

It is important to note that these monitoring channels are carriedindependently on point-to point connections, rather than through anyshared bus such as is provided in the H. 110 protocol for computertelephony.

The backplane also carries I²C buses (SMB protocol) and the LAN wiring.These are carried to each SBC 160-1 etc. either in the J3 position orthe J5 position, depending on the manufacturer of the particular SBC, asdescribed later. The LAN interface module 270 provides the apparatuswith two external LAN ports for communications to the next layer of dataprocessing/aggregation, for example a site processor.

Connectivity is achieved using two LANs (A and B) at 100 BaseT for acardcage. The LAN I/O can be arranged to provide redundant connection tothe external host computer 40. This may be done, for example, by usingfour internal LAN connection and four external LAN connections routedvia different segments of the LAN 60. It is therefore possible to switchany SBC to either of the LAN connections such that any SBC may be on anyone connection or split between connections. This arrangement may bechanged dynamically according to circumstances, as in the case of anerror occurring, and allows different combinations of load sharing andredundancy. Additionally, this allows the probe processors tocommunicate with each other without going on the external LAN. However,this level of redundancy in the LAN connection cannot be achieved if thetotal data from the probe processors exceeds the capacity of any oneexternal LAN connection.

An external timing port (not shown in FIG. 16) is additionally providedfor accurately time-stamping the data in the packet processor. Thesignal is derived from any suitable source, for example a GPS receivergiving a 1 pulse per second input. It is also possible to generate thissignal using one of the Packet Processor cards, where one PacketProcessor becomes a master card and the others can synchronise to it.

The individual modules will now be described in detail, with referenceto FIGS. 17 19. This will further clarify the inter-relationshipsbetween them, and the role of the backplane 190 and chassis 100.

Cross-Point Switch Module 80

FIG. 17 is a block diagram of the cross-point switch 80 and shows alsothe network line interfaces 300 (RX) and 310 (TX) provided on thenetwork interface module 200. There are eight optical line receiverinterfaces 300 provided within module 200. There are thus eight bearersignals which are conditioned on the transition card (module 200) andtransmitted in electrical form EXT 1′-8′directly through the backplane190 to the cross-point switch card 80. Ten individually configurablemultiplexers (selectors) M are provided, each freely selecting one ofthe eight inputs. Each monitoring channel (CH1-8) and hence each packetprocessor 150 can receive any of the eight incoming network signals(EXT1′-8′).

The outputs to the packet processors (CH1-CH4) are via the backplane 190(position J4, FIG. 15B as described above) and may follow, amongstothers, DS3/OC3/OC12/OC48 electrical standards or utilise a suitableproprietary interface. Each packet processor module 150 controls its ownpair of multiplexers M directly.

The external optical outputs EXT 9,10 are provided via transmitinterface 310 of the module 200 for connecting to a spare chassis (as inFIG. 8). These outputs can be configured to be any of the eight inputs,using a further pair of multiplexers M which are controlled by theLAN/Management Module 230. In this way, the spare processor or chassis130 mentioned above can be activated in case of processor failure. In analternative implementation, the selection of these external outputsignals CH9 and CH10 can be performed entirely on the network interfacemodule 200, without passing through the backplane or the cross-pointswitch module 80.

Although functionally each multiplexer M of the cross-point switch isdescribed and shown as being controlled by a respective packet processor150, in the present embodiment this control is conducted via the LAN &management module 230. Commands or requests for a particular connectioncan be sent to the LAN & management module from the packet processor (orassociated SBC 160) via the LAN connections, or I²C buses, provided inconnectors J3 or J5.

Packet Processor Module 150

FIG. 18 is a block diagram of one of the Packet Processor modules 150 ofthe apparatus. The main purpose of packet processor (PP) 150 is tocapture data from the network interface. This data is then processed,analysed and filtered before being sent to a SBC via a local cPCI bus.Packet processor 150 complies with Compact PCI Hot Swap specificationPICMG-2.1 R 1.0, mentioned above. Packet Processor 150 here described isdesigned to work up to 622 Mbits/s using a Sonet/SDH frame structurecarrying ATM cells using AAL5 Segmentation And Reassembly (SAR). Otherembodiments can be employed using the same architecture, for example tooperate at OC48 (2.4 Gbit.s⁻¹).

The following description makes reference to a single “half” of thetwo-channel packet processor module 150, and to a single PacketProcessor/SBC pair only (single channel). The chassis as describedsupports four such Packet Processor/SBC pairs, and each packet processorcomprises two processing means to handle multiple bearer signals(multiple monitoring channels).

It is possible for the Packet Processor 150 to filter the incoming data.This is essential due to the very high speed of the broadband networkinterfaces being monitored, such as would be the case for OC-3 andabove. The incoming signals are processed by the Packet Processor, thisgenerally taking the form of time stamping the data and performingfiltering based on appropriate fields in the data. Different fields canbe chosen accordingly, for example ATM cells by VPI/VCI (VC) number, IPby IP address, or filtering can be based on other, user defined fields.It is necessary to provide the appropriate means to recover the clockand data from the incoming signal, as the means needed varies dependenton link media and coding schemes used.

In a typical example using ATM, ATM cells are processed by VPI/VCI (VC)number. The Packet Processor is provided with means 320 to recover theclock and data from the incoming signal bit stream. The data is then‘deframed’ at a transmission convergence sub-layer 330 to extract theATM cells. The ATM cells are then time-stamped 340 and then buffered ina First In First Out (FIFO) buffer 350 to smooth the rate of burst typedata. Cells from this FIFO buffer are then passed sequentially to an ATMcell processor 360. The packet processor can store ATM cells to allow itto re-assemble cells into a message—a Protocol Data Unit (PDU). Onlywhen the PDU has been assembled will it be sent to the SBC. Beforeassembly, the VC of a cell is checked to ascertain what actions shouldbe taken, for example, to discard cell, assemble PDU, or pass on the rawcell.

Data is transferred into the SBC memory using cPCI DMA transfers to adata buffer 380. This ensures the very high data throughput that may berequired if large amounts of data are being stored. The main limitationin the amount of data that is processed will be due to the applicationssoftware that processes it. It is therefore the responsibility of thePacket Processor 150 to carry out as much pre-processing of the data aspossible so that only that data which is relevant is passed up into theapplication domain.

The first function of the Packet Processor 150 is to locate theinstructions for processing the VC (virtual channel or) to which thecell belongs. To do this it must convert the very large VPI/VCI of thecell into a manageable pointer to its associated processing instructions(VC # key). This is done using a hashing algorithm by hash generator390, which in turn uses a VC hash table. Processor 150, having locatedthe instructions, can then process the cell.

Processing the cell involves updating status information for theparticular VC (e.g. cell count) and forwarding the cell and anyassociated information (e.g. “Protocol Data Unit (PDU) received”) to theSBC 160 if required. By reading the status of a particular VC, theprocessor can vary its action depending on the current status of that VC(e.g. providing summary information after first cell received). Cellprocessor 360 also requires certain configurable information which isapplicable to all of its processing functions regardless of VC (e.g.buffer sizes) and this ‘global’ configuration is accessible via a globalconfiguration store.

A time stamping function 340 can be synchronised to an external GPS timesignal or can be adjusted by the SBC 160. The SBC can also configure andmonitor the ‘deframer’ (e.g. set up frame formats and monitor alarms) aswell as select the optical inputs (EXT 1-8) to be monitored. PacketProcessor 150 provides all of the necessary cPCI interface functions.

Each packet processor board 150-1 etc. is removable withoutdisconnecting power from the chassis. This board will not impact theperformance of other boards in the chassis other than the associatedSBC. The microprocessor notifies the presence or absence of the packetprocessor and processes any signal loss conditions generated by thePacket Processor.

Single Board Computer (SBC) Modules 160

The SBC module 160 is not shown in detail herein, being ageneral-purpose processing module, examples including the MotorolaCPV5350, FORCE CPCI-730, and SMT NAPA. The SBC 150 is a flexible,programmable device. In this specific embodiment two such devices mayexist on one cPCI card, in the form of “piggyback” modules (PMCs). The100 BaseT interfaces, disk memory etc. may also be in the form of PMCs.As already described, communications via the cPCI bus (J1/J2) on theinput side and via the LAN port on the output side and all otherconnections are via the backplane at the rear, unless for diagnosticpurposes for which an RS-232 port is provided at the front.

LAN & Chassis Management Module 230

FIG. 19 is a block diagram of the combined LAN and chassis managementcard for the network probe as has been described. Module 230 performs anumber of key management functions, although the probe units 150/160 canbe commanded independently from a remote location, via the LANinterface. The card firstly provides a means for routing probe units SMBand LAN connections, including dual independent LAN switches 500A and500B to route the LAN connections with redundancy and sufficientbandwidth to the outside world.

On the chassis management side, a Field Programmable Gate Array (FGPA)510 within this module performs the following functions:

-   -   (520) I²C and SMB communications, with reference to chassis        configuration storage registers 530    -   (540) ‘magic packet’ handling, for resetting the modules        remotely in the event that the higher level network protocols        “hang up”;    -   (550) environmental control and monitoring of fan speed and PSU        & CPU temperatures functions to ensure optimal operating        conditions for the chassis, and preferably also to minimise        unnecessary power consumption and fan noise;

A hardware watchdog feature 560 is also included to monitor the activityof all modules and take appropriate action in the event that any of thembecomes inactive or unresponsive. This includes the ability to resetmodules.

Finally, the management module implements at 580 “MultivendorInterconnect”, whereby differences in the usage of cPCI connectors pins(or whatever standard is adopted) between a selection of processorvendors can be accommodated.

As mentioned previously, the chassis carries at some locations, cPCIprocessor modules from a choice of selected vendors, but these arecoupled via cPCI bus to special peripheral cards. While such cards areknown in principle, and the processor-peripheral bus is fully specified,the apparatus described does not have a conventional interconnectarrangement for the broadband signals, multiple redundant LANconnections and so forth. Even for the same functions, such as the LANsignals and I²C/SMB protocol for hardware monitoring, different SBCvendors place the relevant signals on different pins of the cPCIconnector set, particularly they may be on certain pins in J3 with somevendors, and on various locations in J5 with others. Conventionally,this means that system designer has to restrict the user's choice of SBCmodules to those of one vendor, or a group of vendors who have adoptedthe same pin assignment for LAN and SMB functions, besides the standardassignments for J1, and J2 which are specified for all cPCI products.

To overcome this obstacle a modular Multivendor Interconnect (MVI)solution may be applied. The MVI module 580 is effectively fourproduct-specific configuration cards that individually route the LAN andSMB signals received from each SBC 160-1 etc. to the correct locationson the LAN/Management cards. One MVI card exists for each processor.These are carried piggyback on the LAN/management module 230, and eachis accessible from the front panel of the enclosure. The backplane inlocations J3 and J5 includes sufficient connectors, pins andinterconnections between the modules to satisfy a number of differentpossible SBC types. Needless to say, when replacing a processor cardwith one of a different type, the corresponding MVI configuration cardneeds exchanging also.

An alternative scheme to switch the card connection automatically basedon vendor ID codes read via the backplane can also be envisaged. In aparticular embodiment, for example, the “Geographic Address” pinsdefined in the cPCI connector specifications may be available forsignalling (under control of a start-up program) which type of SBC 160is in a given slot. The routing of SMB, LAN and other signals can thenbe switched electronically under control of programs in the LAN &management card 230.

CONCLUSION

Those skilled in the art will recognise that the invention in any of itsaspects is not limited to the specific embodiments disclosed herein. Inparticular, unless specified in the claims, the invention is in no waylimited to any particular type of processor, type of network to bemonitored, protocol, choice of physical interconnect, choice ofperipheral bus (cPCI v. VME, parallel v. serial etc.), number of bearersper chassis, number of bearers per monitoring channel, number ofmonitoring channels per probe unit. The fact that independent processorsubsystems are arranged in the chassis allows multiple data paths fromthe telecommunications network to the LAN network, thereby providinginherent redundancy. On the other hand, for other applications such ascomputer telephony, reliability and availability may not be so criticalas in the applications addressed by the present embodiment. For suchapplications, a similar chassis arrangement but with H.110 bus in thebackplane may be very useful. Similarly, the cPCI bus, I²C bus and/orLAN interconnect may be shared among all the modules.

Each aspect of the invention mentioned above is to be considered asindependent, such that the probe functional architecture can be usedirrespective of the chassis configuration, and vice versa. On the otherhand, the reader will recognise that the specific combinations of thesefeatures offers in a highly desirable instrumentation system, whichprovides the desired functionality, reliability and availability levelsin a compact and scalable architecture.

In the specific embodiments described herein, each probe unit comprisingfirst and second processor modules (the packet processor and SBCrespectively) is configured to monitor simplex and duplex bearers. Theinvention, in any of its aspects, is not limited to such embodiments. Inparticular, each probe unit may be adapted to process one or moreindividual bearer signals. In the case of lower speed protocol signalsthe bearer signals can be multiplexed together (for example within thecross-point switch module 80 or network interface module 200) to takefull advantage of the internal bandwidth of the architecture.

1. A multi-channel network monitoring apparatus for the monitoring oftraffic in a broadband telecommunications network, the apparatuscomprising: a plurality of input connectors for receipt of networksignals to be monitored; a plurality of channel processors mountedwithin a chassis, each for receiving and processing a respectiveincoming signal to produce monitoring results for onward communication,the incoming network signals individually or in groups forming channelsfor the purposes of the monitoring apparatus, each channel processorbeing arranged to operate independently of each other and beingreplaceable without interrupting their operation; one or morecommunication connectors for onward communication of said monitoringresults from the channel processors; and a switching unit; wherein theinput connectors are connected to the channel processors via saidswitching unit, the switching unit in use routing each incoming signalto a selected channel processor and being operable to re-route anincoming channel to another selected channel processor in the event ofprocessor outage.
 2. An apparatus as claimed in claim 1, wherein theswitching unit is further operable to connect the same incoming channelsimultaneously to more than one channel processor.
 3. An apparatus asclaimed in claim 1, wherein the channel processors are in the form ofmodules mounted and interconnected on a common backplane.
 4. Anapparatus as claimed in claim 3, wherein said switching unit comprises afurther module mounted on said backplane.
 5. An apparatus as claimed inclaim 3, wherein said input connectors are provided by a commoninterface module.
 6. An apparatus as claimed in claim 3, wherein saidcommunication connectors are connected to the channel processors via acommunication management module and via the backplane.
 7. An apparatusas claimed in claim 6, wherein said connectors and communicationmanagement module provide for said onward communication to beimplemented over plural independent networks for redundancy.
 8. Anapparatus as claimed in claim 6, wherein the backplane provides anindependent connection between each respective channel processor and thecommunication management module.
 9. An apparatus as claimed in claim 6,wherein the channel processors each comprise a self-contained sub-systemof host of peripheral processing modules interconnected via aCPU-peripheral interface in the backplane, the backplane, providing aseparate peripheral interface for each channel processor.
 10. Anapparatus as claimed in claim 9, wherein said CPU-peripheral interfacefor each channel processor includes a compact PCI interface.
 11. Anapparatus as claimed in claim 3, wherein said backplane and modules areprovided in a single rack-mount chassis, which further houses a powersupply and cooling fan.
 12. An apparatus as claimed in claim 1, whereinthe switching unit further provides for routing any of the incomingchannels to a further connector, for processing by a channel processor,external of the apparatus.
 13. A network monitoring system wherein afirst group of multi-channel network monitoring apparatuses according toclaim 1 are connected to receive a plurality of incoming signals,wherein the switching unit of each apparatus in the first group providesfor routing any of its incoming channels to a further connector, thesystem further comprising at least one further multi-channel networkmonitoring apparatus according to claim 1, connected to receive incomingchannels from said further connectors of the first group of apparatuses,the further apparatus thereby providing backup in the event of a channelprocessor failure or replacement within the first group of apparatuses.14. A network monitoring system wherein a plurality of multi-channelnetwork monitoring apparatuses as claimed in claim 1 are connected to alarger plurality of incoming channels via multiplexing means, the totalnumber of channel processors within the monitoring apparatuses beinggreater than the number of incoming channels at any given time, suchthat any incoming channel can be routed by the multiplexing means andappropriate switching unit to an idle channel processor of one of themonitoring apparatuses.
 15. A system as claimed in claim 14, wherein thenumber of channel processors is greater than the number of incomingchannels, by at least the number of channel processors in eachmonitoring apparatus.
 16. A system as claimed in claim 14, wherein saidmultiplexing means includes electronic switches, while inputs andoutputs are converted to and from optical form for interconnectionbetween separate apparatus.
 17. A system as claimed in claim 14, furthercomprising one or more multi-channel optical power splitters, fortapping into active optical communication bearers to obtain the incomingsignals for the monitoring apparatuses.